In the U.S. Pat. No. 5,200,367 on the one hand a description is provided of so-called ceramic enclosures and on the other hand a description is provided of a plastic encapsulation which can be used as a replacement for a ceramic enclosure. In both cases the enclosure is embodied such that the integrated circuit at the side, where the radiation should impinge on the circuit, is open. This open side can be covered thereafter by a separate glass platelet, or, in case the integrated circuit does not comprise any light sensitive components, can be covered by a platelet of another material, such as a metal platelet.
It is considered well known that the use of ceramic enclosures will result into an increase of costs of the ultimate electronic component. Ceramic enclosures are therefore almost exclusively used for components which have to fulfil high requirements. Furthermore the use of a separate glass covering platelet has a number of disadvantages. A special glue or adhesive is necessary to attach the platelet to the respective section of the enclosure. Furthermore it is not possible, without taking further measures, to restrict the incidence of light to a window which is located at a predetermined positioned above the integrated circuit. A further disadvantage remains in the fact that changing temperatures may lead to stress which may cause loosening or burst of the glass platelet or may cause bursting or other damage to the enclosure.
A method whereby instead of a glass cover platelet use is made of a transparent plastic which is moulded into the open space and which fills this space completely, is for instance described in the European patent application EP-0,400,176. The disadvantage of this method is that no use is made of standard (open tooling) basic elements, so that the costs of this method are relatively high.
Additional methods are known, for instance from the Japanese patent application JP60193345, whereby first of all a layer of transparent plastic is deposited onto the semiconductor circuit using a separate mould, which layer after hardening forms the future light window. Thereafter the upper side of this light window is provided with a protection layer and the resulting half finished product is encapsulated using another mould such that the complete enclosure is obtained. Finally the protecting layer is removed from the window. This method has the disadvantage that the method as such has a large number of steps, whereby furthermore two different moulds are necessary to obtain the final result.